1. Field of the Invention
This invention concerns a process for preparing synthetic polycarbonamide filaments having more uniform acid dyeability and filaments so produced. More particularly, it concerns a process of applying a dye-leveling agent to the filaments during their manufacture.
2. Description of the Prior Art
Articles composed of synthetic polycarbonamide filaments, commonly referred to as nylon filaments, are susceptible to nonuniform dyeing, particularly with acid dyes, which can be due to small differences in filament composition, physical structure, denier and other variables. Such differences can originate from inadequate control over filament spinning conditions such as polymer heat history, quenching rate, drawing, finish application and so forth. Such dyeing non-uniformities are particularly severe with washfast, acid dyes having large molecular structures. The large dye molecules do not readily transfer from one dye-site to another as do smaller acid dyes which give level dyeing but which have poorer dye washfastness.
It is known, for example, from U.S. Pat. Nos. 3,538,151, 3,658,460, 3,713,768 and Br. 1,299,777, that anionic dye-leveling agents can improve dyeing uniformity either as dyebath additives or in a bath pretreatment before dyeing. But at the concentrations frequently required to achieve acceptable leveling, such agents tend to increase the dye cycle times and can actually prevent satisfactory dyeing to deep colors and dark shades.